Method and tape for joining plies



l 'g Patented nec. 17, 194s UNITED -STATES PATENT OFFICE emmen AND A'remt Foa JorNlNG runs j Gordon G. Pierson, Lansdale, Pa. l Application January 26, 1940, Serial No. 315.828

" 7 Claims. (Cl. 154-418) 'This invention relates to improvements in l methods of joining sheets of thin wood veneers that are adapted to be applied to a suitable ina-l terial in the manufacture of panelling and other 'veneered products and of securing the sheets to a ply or base. ,The invention relates Valso to the several sheets of thin woodv are laminated byl means of glue. The iaminae of wood forv the aforesaid purpose may consist of whole sheets of wood or may be formed by abutting several smallver pieces and joining them at their edges in order to yield a large sheet. The essential Joining has customarily been accomplished by gluing the edges of the sheets together with ordinary glue or, even more commonly, by gluing a narrow sheet of paper or a type of illm known as a veneer tape.-

which extends over the lateral surfaces of the veneer close to and overlapping the abutting1 edges of the veneer pieces.

In the past there have been several disadvantages to joining the sheets of wood with a paper or a film glued to their lateral surfaces over their contiguous edges.. First, although the veneerappear on the surfaces of the nished laminations wherever the tape has been applied within the glueline.

A third diiilcuity arises because whenever ordinary veneer tapes are used inside' of glue lines, the bond at that point has had an extremely low moisture resistance, regardless of the moistureresistance properties of the glue used in making the lamination. In some types of laminations it has been possible to turn the veneer tapes i. e.,

to apply the tape to the opposite side of the ve' neer from that which faces the base, in order that the tapes may become exposed on the surface of the panel not within the glue lines.. In such cases Y it becomes necessary to-sand or to scrape the surface of the panel for the purpose of removing the tape before the panel can be ilnished. Obviously.drast ic sanding or scraping is not only an expensive operation but may cut through the veneer and impair the panel.

. 2 The object oi this invention is to eliminate broadly these usual undesirable features by making a veneer tape in a manner to be described subsequently.

A further object is to impregnate a tape with a glue suited to the glues used for uniting veneer to its base so that the band between theone sidel of the -tape and the veneer and also the bond between theA tape and the base may be strengthened by the impregnation and'made equally effective `and the impregnation may protect the tape from weakening by moisture.

A further object is to strengthen and protectl the tape by impregnation and not only to improve the tape surface for gluing purposes but to make the two sides equallyeii'ective for'r glue reception. A further object is to form sturdler panels than before, which therefore may be subjected to vigcrous handling during shipment and installation. Accordingly, not-,only is undue waste of material avoided but `considerable `time lis conserved in working with laminated sheets that are now less subject to injury by the mishaps and the exigencles of'promivscuous handling. Y

A further object is to strengthen'thehold of- .an adhesive by setting up a glue lgradient tapering oir from a full concentration outside the tape to a weaker glue in the middle ofthe tape thickness.

An additional object is to produce a moistureresistant or moisture-proof panel whenever the veneer tape is 'used within the glue line.

For the purpose of illustrating the invention,

the accompanying drawing illustrates several forms which'are at present preferred, since the same have'been found in practice to give satisfactory and reliable results, although it is to be understood that the several'mstrumentauues of the invention can be variously arranged and organized and that the invention is not limited to the precise arrangement and organization of the instrumentalities as herein shown and described.

The invention relates to several other novel 'features of construction andfadvantage appear- 4ing as hereinafter described and claimedv in connection. with the accompanying drawing in l the under side ready `for gluing to a base-which is also shown.

Figure 3 is a section corresponding generally to Figure 2 but with the parts applied and with a base having alayer of veneer already applied and -showing corresponding layers of veneeron the` opposite face of the base.

Figure 4 is a section much like Figure-V 3 but,

i and 2, I' and '2' represent pieces of veneer n which abut at their edges, I against 2, and in an.

other layer I against 2', and which form parts respectively oi?l larger sheets, the several pieces being held together by veneer tape 3 engaging the surfaces at 4 and .5 on opposite sides of the r line of veneer juncture 6. Meeting edges at 6 may be and in many cases are joined by glue. The tape is used to hold the pieces together in order that the larger veneer sheets which are to be applied, may be handled as sheets. High effectiveness canbest be secured and maintained with a tape which is as thin as practicable.

In the prior art veneer held together by tape normally was applied to the base such as 1 with the tape down as in Figures 2 and 3, bringing the tape within the glue line butin some instances it was applied to a base with the tape facing away from the base, as would be the 'case if the sheet of Figure 1 were applied as are the pieces I' and 2 in Figure 4.

Where the tape is on the side of the veneer away lfrom the glue line it is necessary to remove the tape by sanding or scraping unless another ply is to be, added.

My invention is directed primarily to the use of the tape between two plies, whether between the veneer and the original base, or between two sheets of veneer. I have invented also a new tape.

The word base is used here generically without regard to whether the ply in question be a single ply only, as in Figure 2, or whether before the application of the veneer the initial base in question has received-one or4 more layers or plies of veneer as in Figure 3.

In both of Figures 2and 3"the position of the tape when theyeneer hasbeen applied is con sidered to be within the glue 1ine, nottrue with the position in Figure 1; and this isv still true whether the tape be located so as to cover the Joint between the adjacent veneer strips as in al1 of the figures, or for some reason be applied where-there is no joint, but only a recognized possibleweakspot 6'. It is also true that the tape is within the glue line where it has been carried on the outside of a. first ply of veneer as at 3 in Figure 4 which is covered by a second or outer veneer ply, or is glued initially` to the inside" of a second veneer plyas in Figure 3.

lThe veneer tape 3 consists of a very'thin sheet or lm of a porous, permeable and flexible material which has been impregnated by a strong adhesive. Such an impregnating adhesive should have the characteristic of being tenacious not only to the veneer tape `itself but to the glue that is subsequently employed to make the lamination i. e. to hold-the veneer to the base. To distinguish, this will be called the laminating glue.

Preferably the veneer tape is very thm. sur

would be effective because verystro'ng and sufficiently porous but is too expensive for normal use. The material vused for veneer tape must be free from anypriori surface treatment that lwould tend to prevent complete impregnation'of the fibers throughout vthe thickness orf-the tape or nlm. kThis means that there must not be any.

appreciable amount of sizing in the paper as manufactured.'V 'l F01 impregnang the tape the adhesives which have been most satisfactory in tests made by me 4 f have been "animaP glue and -Both of these are-regardedin this description as ni-q trogenous glues of animal origin. For some purposes good 4fish glue-also regarded by me as coming within the genus of nitrogenous glue of animal originis "satisfactory, but the poorer qualities of fish glue are not wholly satisfactory.-

Starch can be used but is not as good as animal pregnation be the same as 4but more dilute than 15 the adhesive used to unite-the tape to the veneer sheets. In this arrangement the impregnating and tape-applying adhesives unite to ygive a progressively variant concentration of adhesive from the impregnating strength present at the middle of the thickness of the tape and increasing in strength toward the surface of the tape. My tests have indicated that the best .results are secured with what is known in the trade as animal glue,- as distinguished from fish glue and casein. For

convenience in 'grouping adhesives together for tion and the excess of the impregnating adhesive is squeezed out of the paper by passing the paper between pressure rolls. I'he squeezing between the rolls tends also to squeeze the remaining adhesive very thoroughly into and or other tape material. r

'I'he weakness of prior paper tapes which were affected by moisture lay primarily in the lack of complete impregnation with glue, permittingfthe weakness of the'unimpregnated central plane of the tape to be emphasized by moisture taken up by the tape. vin two ways; both because the impregnated paper is stronger than the paper was before impregnation, and because the glue does not take up moisture as rapidly as would-the paper if unprotected by the glue. The impregnating glues are preferably nitrogenous glues; this term covering animal glue as.y known in thetrade, ilsh glue and casein. lAll of these glues as well as starch glue hold well to the chief laminating glues, which are casein, r

'starch glue and urea-formaldehyde.

'I'hough my purpose is not primarily to moisture-proof, and the impregnatingglues which I have described are not in themselves moistureproonng glues, it is nevertheless true that where a formaldehyde-containing laminating glue is used, the formaldehyde from this laminating glue affects the impregnating glue and tends to moisture-proof it. Of the impregnating glues named,

casein is -very much more nearly moisture-res istant than animal glue.

In .the preferred embodiment of the tape" will be impregnated with animal glue (the product commercially known as suchj of comparatively high dilution, subsequently coated-- with animal glue of higher concentration for join-fl through the pap'er Impregnaticn protects against this the invention,

it into strips to be moistened and applied hot or cold or by handlingthe individual strips sepa? rately, impregnating them and printing glue on them as they are being appliedtoA the veener at the edges, without any necessity for intermediate I drying.

In accordance with the invention aspreviously 415' specied the following examples obtained from actual practice are hereby' submitted:

vli'aample 1.--A thin sheet of .unsized paperis dipped into ahot 10:1, solution of animalglue.y

The paper is then removed, 'the excess glue is squeezed out and the completely impregnated iilm isdried and cut into strips of suitable size. One side of the film may now receive a surface coat of a more concentrated solution of animal glue and this side may be applied to the veneer surfaces in the customary manner in order that a single sheet consisting of several pieces of veneer is `in condition to be assembled with other sheets to iorm a lamination or a panel. To form the lamination, the single sheets composed of several pieces of joined, veneer arecoated, or the base ma'- terial is, with the laminating glue and pressed in the conventional manner. Both may be coated.

The strength of the bond between the impregnated tape and the sheets of veneer in the nished lamination or plywood is as great as or greater.

than that between the untaped sheets of wood and is deillnitely much4 stronger than anything ever Example 2.--As has been previously mentioned, many kinds and `combinations of strong glues sixteen '0f Watertoone ofgluathe-best I results using about ten parts of water. toone 'of glue. "I'l'iepreferable limit of dilution will be twelve to one. 'Ihese` were animal glues-and the same proportions are correct for'casein and good I fish glues. l Not only isfthere an advantage in using the same adhesive forl impregnation and subsequently Y for holding the tape to the sheets of lveneer of a single ply, animal glue to animal glue', or casein to casein but the impregnated surface on' the opposite side more readily receives the laminating glue. In a variant form of theinvention, unsized and preferably also uncalendered paper is coated with a glue or nitrogenous glues ofanlmal kingdoin origin to glue together two veneer sheets to make a ply without prior impregnation and then a laminating glue as mentioned above is applied using such a high pressure as to force the'laminating glue to impregnate the unsized paper.

`other cases mentioned should 'be quite thin', of

thehord'er of one. two or three thousandths of an inc A While the construction as shown and described is the preferred embodiment of the device, never'- Atheless the same may be modified in detail with-l out departing from the spirit anclthe 'scope' ci.' the invention as defined inthe annexed claims.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

1. The method of joining veneer strips to a I base by adhesives using a strip of unsized porous material, which consists in impregnating the strip, prior to assembling the veneer strips, with one concentration of nitrogenous adhesive-of animal kingdom origin which becomes sticky when mois-V tened to make la tape having the two faces of the tape alike, and cause each to present a surface which will readily bond with adhesive without rendering the body of the tape impervious may be used for impregnating theillm or tape assembly becomes' water resistant because of the formaldehyde that is heat.

With laminating glue it is desirable to have as little water as possible and the proportion may we li be about two parts of water t'o one of glue. On the other hand with impregnating glue the strengths which I have found desirable range from-about iive parts of water to one of glue to released from the resin by to moisture, in gluing the tape .toisurfaces of the i abutting veneer strips and across the joint in the veneer to hold strips of .veneer together into a sheet using the same type of adhesive which becomes sticky when moistened but of greater con-` .2. A woodworking veneer tape comprising an unsized paper strip impregnated with an adhesive which becomes sticky when moistened of a concentration of from about ve to sixteen partsof water to one of adhesive and a 'ply oiwood glued 4same character as the adhesive used in the lmf- A to one side of the paper strip by adhesive of the pregnation and of greater concentration than that used in the impregnation.

3. The method of moisture-proofing the adhesive used for holding a tape to plies of veneer to be secured to a lbase which consists in impregnating tape of unsiaed paper with an adhesive prior to attachment to'the veneer, uniting the tape to the veneer by the same kind of adhesive and gluing the taped veneer to the base by a glue which contains moisture and which liberates formaldehyde, whereby the moisture tends to remoisten the tape adhesives and the formaldehyde in due time tends to moisture-proof the adhe` sive in the tape and, through it, the adhesive holding the tape to the veneer.

4. The method of uniting plies of wood which ananas consists in gluing to veneer sheets making up a single ply, a tape of med paper freely permeable -to glue and moisture ifrom one side to the other. gluing together the plies'under heavy pressure and impregnating the unsized paper by laminating glue containing moisture used between Y the plies due to the action` of the-pressuravthe moisture of the laminating glue and the laminating glue being free to penetrateA into the paper. 5. The method of joining veneer strips to a base by adhesives using a tape of'moisture and glue permeablev paper, which comprises coating the permeable paper of the tape with a cold setting tape-adhesive which becomes sticky when moist, without renderingthe tape impervious to moisture, moistening the tape adhesive and while it is moist gluing the tape to surfaces oi' abutting veneer strips to hold the strips together into a sheet, still without rendering the tape impervious to moisture, and gluing the composite sheet of veneer thus formed to the base, under pressure, with the tape within the glue line, by a laminating adhesive containing moisture, whereby the moisture of the laminating adhesive is free to penetrate to and remoisten the tape adA hesive while under the laminating pressure.

6. The method of joining veneer strips to a base by\adhesives-using a tape 'of moisture and glue permeable paper, which 'comprises coating and permeating the permeable paper of the tape with a cold setting tape adhesive which becomes v sticky when moist, without rendering the tape impervious to moisture, moistening the talle B dhesive and while it is moist gluingthe tape to surfaces of abutting veneer strips vto hold the strips together into a sheet, still without rendering ythe tape impervious to moisture and gluing .thecomposite sheet of veneer thus formed to the base, under pressure, with the tape .within the glue line, by a laminating adhesive containing moisture, whereby the moisture of the laminating adhesive is free to penetrate to and remois, ten the tape adhesive whlle'under thelaminating pressure. Y

l 7. The method ofjolning veneer strips to a base by adhesives, using a tape of moisture and glue permeable paperVwhich comprises coating the permeable paper of thetape with a cold setting tape adhesive which becomes sticky when l moist, without rendering Ithe tape impervious to moisture, moistening the tape adhesive and while.

it is moist gluing the tape to surfaces o! abutting veneer strips to hold the strips together into a sheet, still without rendering the tape impervious y to moisture, and gluing the composite sheet oi' veneer thus formed to the base under pressure,

with the tape within the glue line, by a laminating adhesive containing moisture and-liberating formaldehyde, whereby the moisture of the laminating adhesive is free to penetrate' to and rem'oisten the tape adhesive 'while under the laminating pressure and the formaldehyde in due time tends to make the 4assembly moisture resistant.

, GORDON G. PIERSON. 

